Implantable medical devices such as stents, blood filters, artificial heart valves and the like are typically subjected to hostile working conditions. For example, stents and blood filters are introduced into the body while in a compressed shape and are thereafter expanded via self expansion or mechanical expansion to a final, useful shape when positioned to a target location within the body. After deployment, the devices should have sufficient physical, biological and mechanical properties to perform throughout the expected useful lifetime. Moreover, implantable medical devices are typically characterized by complex, intricate shapes and strict dimensional and compositional tolerances.
In view of the stringent requirements of medical devices, the processes used to form these devices must be accurate and reproducible, and obtain the desired dimensional, compositional and mechanical properties. Conventional production processes, however, are often complex and expensive. For example, conventional processes used to produce patterned stents often start with wire, tube or sheet materials. Typical processing steps to produce a patterned stent from a wire may include winding the wire around a mandrel into a complex configuration, welding the wire at certain junctions, and heat treating the wire to create the final patterned device. To produce a patterned stent from a tube or sheet, conventional processes may include steps such as stamping, cutting or etching a pattern into the starting material, expanding and/or rolling the starting material into a suitable stent shape, and heat treating to create the final device.
Most of the manufacturing steps associated with these conventional methods introduce defects into the metallic structure of the formed device. The defects can include excessive oxidation, localized deformation, surface flaws and the like. These defects often reduce desired properties, such as strength, fatigue resistance and corrosion resistance.
The performance properties of the medical device are not only effected by manufacturing processes, but are also effected by the material properties of the raw material. For instance, if the wire or tube used to form a medical device contains material or structural defects, the formed medical device may also often contain similar or greater defects. Some defects in the formed device may be reduced by techniques, such as annealing, but these techniques often impart other undesirable effects. For instance, annealing often requires high temperature treatment of a metallic device to recrystallize its microstructure to reduce grain size and residual stress. Such a high temperature treatment can often impart physical deformation of the device due to thermal heating and cooling steps or due to the change in the microstructure itself. Because medical devices often require intricate shapes and strict dimensional tolerances, physical deformation of the device during manufacturing is often a problem.
Furthermore, the compositional properties of the raw material used to form the medical device also effects the final properties of the device. Impurities often degrade useful mechanical properties, reduce corrosion resistance and effect the biocompatability of the medical device.
Accordingly, a need exists for a manufacturing process to form a medical device without the disadvantages of the prior art. Furthermore, a need exists for a medical device with improved biocompatability and mechanical properties.
In view of the shortcomings of conventional medical device manufacturing processes, there exists a need for a process that facilitates the reproducible production of medical devices having improved mechanical properties.